The present invention relates to printing plates. In particular, it relates to a printing plate system wherein the image is produced by peel-apart process.
In the printing field, it is sometimes desirable to directly produce lithographic plates. This eliminates the need for an image development processor and a wet developer.
At present time, there are two liabilities to the use of printing plates. First, a processor is needed for image development, which is both expensive for the customer and the vendor and requires significant floor space. Second, a wet developer is normally used, which is messy and often contains ingredients which are or may eventually be classified as hazardous.
In the present invention, the need is eliminated for both a development processor and a wet developer by dry developing the printing plate by a peel-apart process. After exposure, the plate is developed by peeling off a disposable development sheet. This eliminates the messy handling and potential environmental problems associated with liquid developers. Furthermore, no floor space or special plumbing are needed, since the processor has been eliminated.
U.S. Pat. Nos. 4,210,711, 4,334,006 and 4,396,700 cover peel-apart printing plates. All disclose a peel-apart process for forming an image. The processes eliminate the wet processor, but require a laminator, which is normally not needed for developing printing plates. These systems consist of a photosensitive layer coated on a grained/anodized aluminum plate. A film separation is brought into intimate contact with the photosensitive layer and exposed to UV. After exposure, the laminate film is laminated onto the photosensitive layer and the exposed or unexposed areas are peeled-off. The photosensitive composition in these patents is comprised of diazonium salts and various binders. The peel-development sheet is laminated to the photosensitive composition after exposure. When peel-developed, the adhesive layer on the laminate film is completely removed.
The present invention utilizes a photosensitive composition containing a photopolymerizable monomer, a binder, a photoinitiator and at least one colorant. Lamination of the peel-development sheet occurs before exposure preferably during manufacture of the plate. When peel-developed, the adhesive layer remains on the image areas on the aluminum plate and is removed in the non-image areas with the carrier. This ensures that the consumer will not need a laminator to use the product.
Dupont's U.S. Pat. Nos. 4,489,153 and 4,489,154 disclose a peel-apart process used only for color proofing. In this process, a Mylar sheet is coated with a photosensitive composition. This film is then laminated by the customer to a receiver base and then exposed through the Mylar sheet. Peeling off the Mylar sheet develops the image.
The present invention relates to a photosensitive assembly consisting of a film coated on a printing plate, e.g. aluminum, with a development sheet covering the photosensitive film. The assembly is exposed through a mask, and the development sheet is peeled off to remove the unexposed areas. The exposed areas remain to form an ink-receptive image.